Patent Document 1 describes a configuration including a selective catalytic reduction (SCR) catalyst, an adding valve that adds a urea aqueous solution to exhaust gas flowing into the SCR catalyst, and a low pressure EGR (exhaust gas recirculation) system that guides a part of the exhaust gas (EGR gas) from an exhaust passage at a downstream side of the SCR catalyst to an intake passage.
Patent Document 2 describes a configuration including an SCR catalyst, an adding valve that adds a urea aqueous solution to exhaust gas flowing into the SCR catalyst, and a low pressure EGR system that guides a part of the exhaust gas from, an exhaust passage at a downstream side of the SCR catalyst to an intake passage. Patent Document 2 also describes a technique for reducing an amount of EGR gas when adding a urea aqueous solution from the adding valve.
Patent Document 3 describes a configuration including an SCR catalyst, an adding valve that adds a urea aqueous solution to exhaust gas flowing into the SCR catalyst, and a low pressure EGR system that guides a part of the exhaust gas from an exhaust passage at a downstream side of the SCR catalyst to an intake passage. Patent Document 3 also describes a technique for supplying a urea aqueous solution from the adding valve while EGR gas is being recirculated when it is necessary to neutralize condensed water that is present in a pathway of low pressure EGR gas.
Patent Document 4 describes a configuration of a spark ignition internal combustion engine including an apparatus that supplies ammonia to an intake passage and an SCR catalyst arranged in an exhaust passage,